If you rotate your camera around some randomly chosen point, your images will have [[parallax]] and your stitches will be bad.

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{{Glossary|The special point that you have to rotate your camera around, to avoid parallax errors. Commonly (and falsely) referred to as the [[Nodal Point]].}}

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If you rotate your camera around some randomly chosen point, your images may show [[parallax]] and be difficult to stitch.

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With most lenses, there is one special point around which you can rotate your camera and get no parallax.

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With most lenses, there is one special point around which you can rotate your camera and get no parallax. This special "'''no-parallax point'''" is the center of the lens's '''entrance pupil''', a virtual aperture within the lens. In the panorama photography community, this special point is often called the "'''nodal point'''", but it is in fact unrelated to the actual nodal points of the lens.<sup>[[#References|1]],[[#References|2]]</sup> The actual nodal points are other points on the optical path, which are of no significance to most photographers. The no-parallax point is also the "center of perspective", but this term is not commonly used and does not describe why the no-parallax point is important.

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In the panorama photography community, that special '''"no-parallax point"''' is often called the '''"nodal point"''' or '''"entrance pupil".'''

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The entrance pupil is the image of the limiting aperture or diaphragm, as seen through the front of the lens. The image seen may be magnified by the effect of the lens elements in front of it, and the image is displaced from the actual position of the aperture. It is the center of this image about which the camera must be rotated to avoid parallax. Interestingly, the entrance pupil is important in another way: the [[f-number]] of a lens is actually the ratio of the [[Focal Length |focal length ]] to the diameter of the entrance pupil, not to the diameter of the physical aperture inside the camera.

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Periodically there is debate about what it ''ought'' to be called. In optics, the term "nodal point" means something else entirely, a place in the optical path that is of no significance to most photographers. The term "entrance pupil" means the image of the limiting aperture, as seen through the front of the lens. "Entrance pupil" properly refers to an area, not a point, but the no-parallax point is at the center of the entrance pupil so these terms are closely related. The no-parallax point is also the "center of perspective", but this term is not commonly used and does not describe why the no-parallax point is important.

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Everything considered, the best term for the no-parallax point may be (surprise!) the "no-parallax point". "Entrance pupil" is correct although a bit imprecise to a geometry purist; it makes a good term for searching the literature and would be preferred in formal writing. "Nodal point" is commonly-used, but incorrect and leads to confusion. It should be avoided when writing and interpreted with caution in reading the literature.

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Everything considered, the best term for the no-parallax point may be (surprise!) the "no-parallax point". "Entrance pupil" is accurate although a bit imprecise; it makes a good term for searching the literature and may be preferred in formal writing. "Nodal point" is ambiguous and potentially confusing. It should be avoided when writing and interpreted with caution in reading the literature.

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Regardless of what you call the no-parallax point, it is easily found by trial and error. Just adjust the rotation point so that foreground and background points stay lined up.

Regardless of what you call the no-parallax point, it is easily found by trial and error. Just adjust the rotation point so that foreground and background points stay lined up.

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Some lenses, notably fisheyes, do not have a single no-parallax point. Instead, they have a range of what we might call "least-parallax points" that depend on the angle away from the lens axis. Such lenses can be recognized easily -- just look into the front of the lens and observe that the location of the entrance pupil moves forward or back as you rotate the lens off-axis. With such lenses, it is good to pick one angle at which you like to stitch, and rotate your camera around a point that gives no parallax at that angle.

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Some lenses, notably fisheyes, do not have a single no-parallax point. Instead, they have a range of what we might call "least-parallax points" that depend on the angle away from the lens axis. Such lenses can be recognized easily — just look into the front of the lens and observe that the location of the entrance pupil moves forward or backward as you rotate the lens off-axis. With such lenses, it is good to pick one angle at which you like to stitch, and rotate your camera around a point that gives no parallax at that angle.

To facilitate finding the no-parallax point for other people, please fill the measurements you have found for your Camera / Lens / Focal Length combination in the [[Entrance Pupil Database]]

To facilitate finding the no-parallax point for other people, please fill the measurements you have found for your Camera / Lens / Focal Length combination in the [[Entrance Pupil Database]]

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== Links ==

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==See also==

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*[[NPP adapters]]

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*[[Entrance Pupil Database]]

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Big Ben's Panorama Tutorials, [http://www.path.unimelb.edu.au/~bernardk/tutorials/360/photo/nodal.html Determining the Nodal Point of a Lens].

[http://michel.thoby.free.fr/ Michel Thoby], especially [http://michel.thoby.free.fr/SIGMA8mm/Alpha%20test%20300D/Nodal%20point%20of%20SIGMA%208mm.html Nodal point location for the SIGMA 8mm f:4 lens], which describes an interesting approach using a laser pointer.

[[Category:Glossary]]

[[Category:Glossary]]

Latest revision as of 03:14, 13 March 2012

If you rotate your camera around some randomly chosen point, your images may show parallax and be difficult to stitch.

With most lenses, there is one special point around which you can rotate your camera and get no parallax. This special "no-parallax point" is the center of the lens's entrance pupil, a virtual aperture within the lens. In the panorama photography community, this special point is often called the "nodal point", but it is in fact unrelated to the actual nodal points of the lens.1,2 The actual nodal points are other points on the optical path, which are of no significance to most photographers. The no-parallax point is also the "center of perspective", but this term is not commonly used and does not describe why the no-parallax point is important.

The entrance pupil is the image of the limiting aperture or diaphragm, as seen through the front of the lens. The image seen may be magnified by the effect of the lens elements in front of it, and the image is displaced from the actual position of the aperture. It is the center of this image about which the camera must be rotated to avoid parallax. Interestingly, the entrance pupil is important in another way: the f-number of a lens is actually the ratio of the focal length to the diameter of the entrance pupil, not to the diameter of the physical aperture inside the camera.

Everything considered, the best term for the no-parallax point may be (surprise!) the "no-parallax point". "Entrance pupil" is correct although a bit imprecise to a geometry purist; it makes a good term for searching the literature and would be preferred in formal writing. "Nodal point" is commonly-used, but incorrect and leads to confusion. It should be avoided when writing and interpreted with caution in reading the literature.

Regardless of what you call the no-parallax point, it is easily found by trial and error. Just adjust the rotation point so that foreground and background points stay lined up.

Some lenses, notably fisheyes, do not have a single no-parallax point. Instead, they have a range of what we might call "least-parallax points" that depend on the angle away from the lens axis. Such lenses can be recognized easily — just look into the front of the lens and observe that the location of the entrance pupil moves forward or backward as you rotate the lens off-axis. With such lenses, it is good to pick one angle at which you like to stitch, and rotate your camera around a point that gives no parallax at that angle.

To facilitate finding the no-parallax point for other people, please fill the measurements you have found for your Camera / Lens / Focal Length combination in the Entrance Pupil Database